Backpack



FIG. 1 is a front perspective view of a backpack showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof; and,

FIG. 6 is a rear perspective view thereof.

The structural features depicted by broken lines in the drawing have been shown for the purpose of illustrating portions of the backpack that form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 